1. Field of the Invention
The invention relates to a wheel rim, more particularly to a bicycle wheel rim.
2. Description of the Related Art
As shown in FIG. 1, a conventional bicycle wheel rim 1 for retaining a tire 11 and a plurality of spoke fastening components 10 comprises a pair of opposite annular side walls 12 that are spaced apart from each other, and that surround a horizontally disposed rim axis (not shown), respectively. Each of the annular side walls 12 has a radial inner edge 121, and a radial outer edge 122 for retaining the tire 11. The conventional wheel rim 1 further comprises an annular base wall 13 interconnecting the radial inner edges 121 of the annular side walls 12, an annular reinforcing wall 14 interconnecting the annular side walls 12 and surrounding the annular base wall 13, and a pair of opposite annular connecting walls 15 interconnecting the annular base wall 13 and the annular reinforcing wall 14. The spoke fastening components 10 extend through the annular base wall 13 and are disposed between the annular connecting walls 15.
By virtue of the annular connecting walls 15, the strength of the conventional wheel rim 1 is strengthened. However, since the annular base wall 13 and the annular reinforcing wall 14 are formed as arches that open away from the rim axis, the conventional wheel rim 1 is likely to deformunder the application of a lateral thrust force. The drawback is very serious when the conventional wheel rim 1 is applied to extreme sport vehicles that require a wheel rim with a relatively wide and flat radial cross-section, such as jumping bikes and mountain bicycles.
U.S. Pat. No. 6,817,680 B2 discloses another conventional bicycle wheel rim. As shown in FIG. 2, the conventional wheel rim 2 for retaining a tire 21 and a plurality of spoke fastening components 20 comprises a pair of opposite annular side walls 22 that are spaced apart from each other, and that surround a horizontally disposed rim axis (not shown), respectively. The conventional wheel rim 2 further comprises an annular base wall 23 interconnecting radial inner edges 221 of the annular side walls 22, a pair of annular reinforcing walls 24, and an annular angled wall 25. Each of the annular reinforcing walls 24 has one edge connected to the annular base wall 23, and another edge connected to a respective one of the annular side walls 22. The annular angled wall 25 includes a bend portion 251 and a pair of oblique portions 252 extending obliquely from opposite edges of the bending portion 251 to the annular base wall 23. The spoke fastening components 20 extend through the annular base wall 23, and are disposed between a respective one of the annular reinforcing walls 24 and a corresponding one of the oblique portions 252 of the annular angled wall 25.
By virtue of the annular angled wall 25, the strength of the annular base wall 23 is strengthened. However, since stress forces that are applied to the annular angled wall 25 will concentrate at the bend portion 251, and since the annular angled wall 25 is connected to the annular base wall 23, the conventional wheel rim 2 is also likely to deform under the application of a lateral thrust force. Like the previous conventional wheel rim 1, the drawback is very serious when the conventional wheel rim 2 is required to have a relatively wide and flat radial cross-section.